VALENCE ISOMERIZATION OF QUADRICYCLANE CATALYZED BY BIS(MU-ACETATO)-BIS(NORBORNADIENE)DIRHODIUM - EVIDENCE FOR A RHODOCYCLOBUTANE INTERMEDIATE

Quadricyclane isomerization is catalyzed by red-orange [Rh(NBD)(AcO)]2 to give norbornadiene (75%) and two endo bis(norbornadienes), 1 (23%) and 2 (2%), at 25 °C. The reaction is characterized by the formation and disappearance of yellow Rh(III) intermediates. In CH2C12 at 25 °C the rate law -d[Q] /dt = (0.64 s-1)[Cat]0 adequately describes the results of kinetic studies carried out in the presence of large excesses of Q and NBD and with [Cat]0 > 10-4 M. At -50 °C rhodocyclohexane intermediates in the formation of dimers were detected and characterized by 13H and 1C{1H} NMR spectra. The results are consistent with a stepwise mechanism involving insertion of Rh(I) into a cyclopropyl ring to form a rhodocyclobutane intermediate. © 1979, American Chemical Society. All rights reserved.